title: Synthesis of ultrasmooth nanostructured diamond films by microwave plasma chemical vapor deposition using a He/H(2)/CH(4)/N(2) gas mixture.
abstract: Ultrasmooth nanostructured diamond (USND) films were synthesized on Ti-6Al-4V medical grade substrates by adding helium in H(2)/CH(4)/N(2) plasma and changing the N(2)/CH(4) gas flow from 0 to 0.6. We were able to deposit diamond films as smooth as 6 nm (root-mean-square), as measured by an atomic force microscopy (AFM) scan area of 2 μm(2). Grain size was 4-5 nm at 71% He in (H(2) + He) and N(2)/CH(4) gas flow ratio of 0.4 without deteriorating the hardness (~50-60 GPa). The characterization of the films was performed with AFM, scanning electron microscopy, x-ray diffraction (XRD), Raman spectroscopy, and nanoindentation techniques. XRD and Raman results showed the nanocrystalline nature of the diamond films. The plasma species during deposition were monitored by optical emission spectroscopy. With increasing N(2)/CH(4) feedgas ratio (CH(4) was fixed) in He/H(2)/CH(4)/N(2) plasma, a substantial increase of CN radical (normalized by Balmer H(α) line) was observed along with a drop in surface roughness up to a critical N(2)/CH(4) ratio of 0.4. The CN radical concentration in the plasma was thus correlated to the formation of ultrasmooth nanostructured diamond films.
authors.affiliation: Department of Physics, University of Alabama at Birmingham (UAB), Birmingham, Alabama 35294-1170; and UAB Center for Nanoscale Materials and Biointegration (CNMB), University of Alabama at Birmingham, Birmingham, Alabama 35294-1170.
authors.forename: S
authors.initials: S
authors.lastname: Chowdhury
authors.forename: Damon A
authors.initials: DA
authors.lastname: Hillman
authors.forename: Shane A
authors.initials: SA
authors.lastname: Catledge
authors.forename: Valery V
authors.initials: VV
authors.lastname: Konovalov
authors.forename: Yogesh K
authors.initials: YK
authors.lastname: Vohra